All-wheel drive vs. four-wheel drive: What’s the difference?

A Porsche 911 4S and a Range Rover have little in common, except that they can both send power to all four wheels. But they do so for rather different reasons, and in that lies the subtle difference between all-wheel drive and four-wheel drive.

Getting out to lock the front hubs after it becomes clear you need more bite.

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Four-wheel drive, or 4WD, has its roots in 4x4s: Tough off-roaders like Jeeps and Ford Broncos. You can spot them by the mud and dented body panels.

Slung underneath them is a second gearbox called a transfer case that takes some of the power coming out of the transmission to send to the front wheels. That power is also controlled by a lever for either low or normal gear ratios and all of that goes out to geared hubs you once had to get out and lock by hand for max traction. It made for a muddy excursion when you got stuck.

Today it’s common to find all-wheel drive in a BMW or Lincoln sedan that will never see mud deeper than what accumulates in the curb at Whole Foods.

In passenger cars 4WD is usually referred to as AWD, which is something of a distinction of art. AWD is primarily tuned to allow a street car to have more directional bite in fast corners and to put prodigious power down to the street for high performance. Conversely, 4WD is often called upon at very low speeds, climbing through snow, rocks, gullies or deep mud. But in between those two scenarios lie a lot of common ground like rain or snow where both systems are very good.

In all modern vehicles, the AWD or 4WD system is computer-managed so you need do little or nothing to use it to its full advantage: You should never have to get out and crawl across your hood.

AWD and 4WD remain in the minority compared to the most common car layouts: Front wheel drive (FWD) and rear wheel drive (RWD). Both of those send power to only one pair of the car’s wheels and tires.

Why not put AWD into every car? Cost, weight, complexity and reduced fuel economy are among the reasons, though that has not stopped AWD from flourishing in the passenger car, SUV, crossover and minivan market in the last 20 years.